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Boris Kopeliovich

Publications and source records attributed to Boris Kopeliovich.

At least 19 recordsLinked to original sources
arXiv2023

Abundant radiation of soft photons: a puzzle lasting four decades

The observed enhancement of low-kT photons in comparison with incorrect calculations, should not be treated as a puzzle. The paper by Low considered a large rapidity gap process of diffractive excitation of a hadron, h -> h+γ, rather than multiple hadron production spanning all over the rapidity interval between colliding hadrons. The optical theorem connects these two processes, and what is inner bremsstrahlung, suppressed according to Low, corresponds to radiation from final state hadrons. Thus, the main result of the Low theorem, based on gauge invariance of the diffractive bremsstrahlung amplitude, supplemented with the optical theorem, contradicts the so-called bremsstrahlung model. The latter has been used for comparison with data, leading to the longstanding soft photon puzzle.

hep-ph↗
arXiv2017

Heavy flavor production in high-energy $pp$ collisions: color dipole description

We present a detailed study of open heavy flavor production in high-energy $pp$ collisions at the LHC in the color dipole framework. The transverse momentum distributions of produced $b$-jets, accounting for the jet energy loss, as well as produced open charm $D$ and bottom $B$ mesons in distinct rapidity intervals relevant for LHC measurements are computed. The dipole model results for the differential $b$-jet production cross section are compared to the recent ATLAS and CMS data while the results for $D$ and $B$ mesons production cross sections -- to the corresponding LHCb data. Several models for the phenomenological dipole cross section have been employed to estimate theoretical uncertainties of the dipole model predictions. We demonstrate that the primordial transverse momentum distribution of the projectile gluon significantly affects the meson spectra at low transverse momenta and contributes to the largest uncertainty of the dipole model predictions.

hep-ph↗
arXiv2016

Project X: Physics Opportunities

Part 2 of "Project X: Accelerator Reference Design, Physics Opportunities, Broader Impacts". In this Part, we outline the particle-physics program that can be achieved with Project X, a staged superconducting linac for intensity-frontier particle physics. Topics include neutrino physics, kaon physics, muon physics, electric dipole moments, neutron-antineutron oscillations, new light particles, hadron structure, hadron spectroscopy, and lattice-QCD calculations. Part 1 is available as arXiv:1306.5022 [physics.acc-ph] and Part 3 is available as arXiv:1306.5024 [physics.acc-ph].

hep-ex↗
arXiv2016

Hard hadronic diffraction is not hard

Hadronic diffractive processes characterised by a hard scale (hard diffraction) contain a nontrivial interplay of hard and soft, nonperturbative interactions, which breaks down factorisation of short and long distances. On the contrary to the expectations based on the factorization hypothesis, assuming that hard diffraction is a higher twist, these processes should be classified as a leading twist. We overview various implications of this important observation for diffractive radiation of Abelian (Drell-Yan, gauge bosons, Higgs boson) and non-Abelian (heavy flavors) particles, as well as direct coalescence into the Higgs boson of the non-perturbative intrinsic heavy flavour component of the hadronic wave function.

hep-ph↗
arXiv2015

Diffractive Higgsstrahlung

We consider single-diffractive (SD) Higgs production in association with heavy flavour in proton-proton collisions at the LHC. The main focus of our study is a reliable estimate of SD/inclusive ratio, not a precision computation of the cross sections. The calculations are performed within the framework of the phenomenological dipole approach, which includes by default the absorptive corrections, i.e. the gap survival effects at the amplitude level. The dominant mechanism is the diffractive production of heavy quarks, which radiate a Higgs boson (Higgsstrahlung). Although diffractive production of $t$-quarks is grossly suppressed as $1/m_t^2$, the large Higgs-top coupling compensates this smallness and the Higgsstrahlung by $t$-quarks becomes the dominant contribution at large Higgs boson transverse momenta. We computed the basic observables such as the transverse momentum and rapidity distributions of the diffractively produced Higgs boson in association with the bottom and top quark pair. Finally, we discuss a potential relevance of the diffractive Higgsstrahlung in comparison to the Higgsstrahlung off intrinsic heavy flavor at forward Higgs boson rapidities.

hep-ph↗
arXiv2015

Diffractive Bremsstrahlung in Hadronic Collisions

Production of heavy photons (Drell-Yan), gauge bosons, Higgs bosons, heavy flavors, which is treated within the QCD parton model as a result of hard parton-parton collision, can be considered as a bremsstrahlung process in the target rest frame. In this review, we discuss the basic features of the diffractive channels of these processes in the framework of color dipole approach. The main observation is a dramatic breakdown of diffractive QCD factorisation due to the interplay between soft and hard interactions, which dominates these processes. This observation is crucial for phenomenological studies of diffractive reactions in high-energy hadronic collisions.

hep-ph↗
arXiv2013

Diffractive gauge bosons production beyond QCD factorisation

We discuss single diffractive gauge bosons ($γ^*,\,W^{\pm},\,Z$) production in proton-proton collisions at different (LHC and RHIC) energies within the color dipole approach. The calculations are performed for gauge bosons produced at forward rapidities. The diffractive cross section is predicted as function of fractional momentum and invariant mass of the lepton pair. We found a dramatic breakdown of the diffractive QCD factorisation caused by an interplay of hard and soft interactions. Data from the CDF experiment on diffractive production of $W$ and $Z$ are well explained in a parameter free way.

hep-ph↗
arXiv2011

Diffractive Drell-Yan process: hard or soft?

Single diffractive Drell-Yan reaction in hadron-hadron collisions is considered as an important source of information on the properties of soft QCD interactions. In particular, it provides an access to the dynamics of the QCD factorisation breaking due to the interplay between hard and soft interactions which leads to a nontrivial energy and scale dependence of the Drell-Yan observables. We study the process at forward rapidities in high energy proton-(anti)proton collisions in the color dipole approach. Predictions for the total and differential cross sections of the diffractive lepton pair production are given at different energies.

hep-ph↗
arXiv2006

Diffractive Higgs Production from Intrinsic Heavy Flavors in the Proton

We propose a novel mechanism for exclusive diffractive Higgs production $pp \to p H p $ in which the Higgs boson carries a significant fraction of the projectile proton momentum. This mechanism will provide a clear experimental signal for Higgs production due to the small background in this kinematic region. The key assumption underlying our analysis is the presence of intrinsic heavy flavor components of the proton bound state, whose existence at high light-cone momentum fraction $x$ has growing experimental and theoretical support. We also discuss the implications of this picture for exclusive diffractive quarkonium and other channels.

hep-ph↗
arXiv1998

Charmonium and lepton pair production with medium energy antiprotons

The medium energy antiproton beam facility which is under discussion at GSI offers new opportunities to study the QCD of heavy flavours, nuclear structure and exotic mesons. We discuss these topics and briefly highlight other problems in charm production and proton structure.

hep-ph↗
arXiv1998

Neutron-Antineutron Oscillations in Nuclei Revisited

An upper limit on $n-\bar n$ oscillations can be obtained from the stability of matter. This relation has been worked out theoretically and together with data yields $τ_{n\bar n} > (1 - 2)\times 10^8 sec$. A recent publication claims a different relation and finds a nuclear suppression of the $n\to\bar n$ oscillations which is two orders of magnitude weaker than the previous evaluations. Using the same approach we find, nevertheless, that the earlier estimates are correct and conclude that future experiments with free neutrons from reactors are capable to put a stronger limit on the $n - \bar n$ oscillation time than experiments with large amount of neutrons bound in nuclei.

hep-ph↗
arXiv1998

High-Energy Polarimetry at RHIC

We compare a few types of high energy reactions which seem to be practical for polarimetry at RHIC. Coulomb-nuclear interference (CNI) in pp elastic scattering leads to a nearly energy-independent left-right asymmetry A_N(t) at small t. The systematical uncertainty of this method is evaluated to be ~ 10%. The CNI in proton-nucleus elastic scattering is predicted to result in larger values of A_N(t) and occurs at larger momentum transfer than in pp elastic scattering. This energy independent asymmetry can be used for the polarimetry. As an absolute polarimeter one can use elastic pp scattering on a fixed target at large |t| ~ 1 - 1.5 GeV^2, where A_N(t) is reasonably large and nearly energy independent. Although it cannot be reliably calculated, one can calibrate the polarimeter by measuring the polarisation of the recoil protons.

hep-ph↗
arXiv1996

Interplay of Interference Effects in Production of $J/Ψ$ and $Ψ'$ off Nuclei

Our main observations are: (i) The effective path length of the $c\bar c$ wave packet, which is produced in the nucleus, grows with the energy of the produced charmonium. The variation is controlled by the coherence length $l_c=2E_Ψ/M^2_Ψ$. (ii) A colorless $c\bar c$ wave packet produced in $pp$-interaction is a specific linear combination of the $J/Ψ$ and $Ψ'$ states, and interacts substantially weaker that any of its components. The time evolution of this wave packet is controlled by the formation length, $l_f=2E_Ψ/(M^2_{Ψ'} - M^2_Ψ)$. Exact formulas incorporating with these effects are derived. The interplay of the two phenomena results in a nontrivial energy- and $x_F$-dependence of the nuclear suppression of the charmonium production in proton-nucleus and nucleus-nucleus collisions and explains some of the experimentally observed effects.

nucl-th↗
arXiv1995

Nuclear Shadowing and the Proton Structure Function at Small x

A new scaling variable is introduced in terms of which nuclear shadowing in deep-inelastic scattering is universal, i.e. independent of $A$, $Q^2$ and $x$. This variable can be interpreted as a measure of the number of gluons probed by the hadronic fluctuations of a virtual photon during their lifetime. According to recent data from the H1 and ZEUS experiments, the gluon density in a proton rises steeply as $x$ tends to zero. So nuclei which in the infinite momentum frame have a large surface density of gluons model at larger $x$ values what we expect for the proton at much smaller $x$. Using experimental information on nuclear shadowing we predict the unitarity corrections to the proton structure function at small $x$ and extract the bare Pomeron intercept.

hep-ph↗
arXiv1995

The Relative $J/Ψ$ to $Ψ'$ Suppression in Proton-Nucleus and Nucleus-Nucleus Collisions

We calculate the nuclear suppression for $J/Ψ$ and $Ψ'$ production within a coupled channel approach in the subspace of the $J/Ψ$ and $Ψ'$ states. We are able to explain, why (i) the $J/Ψ$ and $Ψ'$ show the same suppression from $200\ GeV$ to $800\ GeV$ in proton-nucleus collisions and why (ii) the $Ψ'$ is absorbed more strongly than the $J/Ψ$ in nucleus-nucleus collisions at $200\ GeV$. The numerical result which includes only interactions with nucleons acconts for half of the observed suppression in sulphur-uranium collisions.

hep-ph↗
arXiv1994

Nuclear Broadening of Out-of-Plane Transverse Momentum in Di-Jet Production

Recently claimed \cite{dj1,dj2,FC} anomalous nuclear effects in di-jet production are analyzed in view of multiple interaction of projectile/ejectile partons in nuclear matter. We derive model--independent relations between A-dependence of the cross section and nuclear broadening of transverse momentum. Comparison with the data show that initial/final state interaction of partons participating in hard process is hard as well. This is a solid argument in favor of smallness of a color neutralization radius of a hadronizing highly virtual quark.

hep-ph↗
arXiv1993

High $Q^2$ Probe of Nuclear Spectral Function and Color Transparency

Contrary to widespread opinion, color transparency (CT) brings essential ambiguity to, rather than helps in, study of the nuclear spectral function in quasielastic lepton scattering, $A(l,l'p)A'$, at high $Q^2$. Although the nuclear attenuation vanishes, the final state interaction (FSI) of a small-size ejectile wave packet, propagating through nuclear matter, remains. It manifests itself in a substantial, but uncertain, longitudinal momentum transfer to the nuclear medium. We predict a strong Fermi-momentum bias of the nuclear transparency at high $Q^2$, which enters as a factor at the nuclear spectral function, and makes uncertain the results of measuring the high-momentum tail of Fermi distribution.

hep-ph↗